Most agricultural and industrial tractors are two-wheel drive tractors, with rear drive wheels and steerable front wheels. However, there is a trend towards larger, higher horsepower tractors, and with their requirement for greater traction there is a trend toward four wheel drive tractors which are articulated about a vertical axis so that steering is accomplished by swinging one frame section relative to the other frame section. Such four wheel drive articulated tractors are still relatively low-volume production machines as compared to the more conventional two wheel drive tractors and it is therefore desirable that as many components of the four wheel drive tractors as possible be common to the two wheel drive tractor so as to keep the price of tooling and production equipment at a minimum.